This happened to me a few times in my first trimester, but it just happened to me again last night and I am 15 weeks. The cramps
are similar to those I've felt from menstrual cramps
. Lower abdomen, dull and achy. Not sure how long they have lasted because it started when I was asleep, but once it wakes me up I'm up for another 10-20 mins because it makes me uncomfortable and difficult to fall back asleep.